Independent flow rate and droplet size control system and method for sprayer

A flow rate and droplet size control system for a spray system including a spray liquid tank, a pump fluidically connected to the tank, a spray liquid line fluidically connected to the pump and a plurality of nozzle assemblies fluidically connected to the spray liquid line and each having a nozzle valve movable between open and closed positions and a nozzle tip, which independent flow rate and droplet size control system comprises:

• (a) a setpoint conversion subroutine receiving as inputs a flow rate setpoint and a volume median droplet size setpoint and providing as outputs a duty cycle setpoint and a liquid pressure setpoint, said setpoint conversion subroutine including means for independently controlling the flow rate and droplet size;
• (b) an application rate control subsystem receiving said duty cycle setpoint from said setpoint conversion subroutine and including a flow controller with function generation means for generating control signals for said nozzle valves corresponding to duty cycles thereof and a flow meter fluidically connected to said spray liquid line;
• (c) said flow controller, nozzle valves and flow meter forming a closed-loop feedback subsystem for maintaining a relatively constant flow rate;
• (d) a droplet size control subsystem receiving said liquid pressure setpoint from said setpoint conversion subroutine and including a pressure controller, pressure control means in said spray liquid line for controlling pressure therein and receiving a pressure control signal from said pressure controller and a liquid pressure transducer in said spray liquid line providing a signal corresponding to a liquid pressure therein to said pressure controller;
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• (e) said pressure controller, said pressure control means and said liquid pressure transducer forming a closed-loop feedback subsystem for maintaining a relatively constant liquid pressure in said spray liquid line.

A flow rate and droplet size control method for a spray system including a spray liquid source, variable discharge pressure control means associated with said spray liquid source and a nozzle assembly with a nozzle tip for discharging said spray liquid and a nozzle valve movable between open and closed positions, which comprises the steps of:

• (a) inputting flow rate and volume median droplet size setpoints;
• (b) outputting a liquid pressure setpoint;
• (c) adjusting said pressure control means in response to said liquid pressure setpoint;
• (d) outputting a duty cycle setpoint for said nozzle valve;
• (e) adjusting the duty cycle of said nozzle valve assembly corresponding to the timing of cycles thereof between open and closed positions in response to said flow rate setpoint;
• (f) providing a setpoint conversion subroutine for receiving said flow rate and volume median droplet size setpoints as inputs;
• and
• (g) independently controlling said duty cycle setpoint and said liquid pressure setpoint for providing independent flow rate and droplet size control.